Mill rolling machine



March 31, 1970 N. H. POLAKOWSKI 3,

MILL ROLLING MACHINE Filed April 20. 1967 FIG. 1'

/N VENTOR by flazafi. P azowski ,2

- aiiys United States Patent 3,503,242 MILL ROLLING MACHINE Natalis H.Polakowski, 226 Laurel Ave., Wilmette, Ill. 60091 Filed Apr. 20, 1967,Ser. No. 632,421 Int. Cl. B21b 13/14 US. Cl. 72241 9 Claims ABSTRACT OFTHE DISCLOSURE The invention resides in a mill roll and machineembodying same for use in the production of flattened sheet, plate orstrip in which the roll is in the form of a composite having a hardenedmetal outer shell, a steel arbor and a thin layer of resilient materialbetween the shell and arbor whereby the working surface of the workingroll in engagement with the material can conform to the profile of thematerial processed through the machine to effect uniform reductionpercentage-wise crosswise of the material.

This invention relates to the production of sheets, strip, or platehaving a high degree of flatness and it relates more particularly to thedesign and construction of rolls and to machines embodying such rollsused in the production of flat-rolled products. Strip and sheet rollingmills and tension roller levelers will be used in the following asexamples of such equipment although other applications will becomeapparent from the description of the principles. Whereas the inventionhas particular application to the processing of metals, its basicconcepts have corresponding application to strips and sheets of othermaterials, such as plastics, and it is intended to include same.

To maintain perfect flatness in rolling of sheet and related products,the material must be reduced by equal percentages of the originalthickness across the entire width. In present practice, this conditioncannot be achieved owing to the mismatch between the roll gap geometryand the actual profile of the incoming sheet which varies, depending onits position along a coil, its width, wear of rolls in the hot and coldmills, in which it has previously been processed, and other factorsknown in the trade. As a result, once the relative position of the twowork rolls in a stand is fixed by setting the screwdown, the flatness ofthe material issuing therefrom will vary because the relatively rigidrolls will tend to iron out and hence excessively elongate areas thatare thicker than average while causing less than needed reduction ofthinner than usual areas. In either case edge waves, center buckles, andsimilar defects will result.

The geometry or profile of the roll gap is a function not only of theposition of the screwdown mechanism but also the camber of the workrolls. The camber denotes the diiference between the actual profile ofthe work roll in the no-load condition and a straight line drawn betweenthe extreme points of the working surface of the roll parallel with itsaxis. This camber is occasionally zero but more often convex to theoutside. Under the rolling load, the rolls deflect and the deflectionlines then delineate the roll gap and define the cross-sectional form ofthe reduced strip or plate. This form, however, does not normallysatisfy the basic requirement of flatness for it does not provide equalpercent reductions at each location across and along the material.

In order to obviate this difliculty various roll bending devices weredeveloped to optimize, as far as possible, the roll gap geometry.Irrespective of their construction, these devices suffer from at leasttwo basic deficiencies, namely (1) they must be continuously manuallyadjusted in response to the visual judgment of the operator who watchesthe issuing sheet, and (2) they can provide only a simple profilecorrection by fiexure of the contact line into a uniformly convex orconcave form. The former gives a subjective error coupled with a randomlag in its corrective action. The latter is incapable of accommodatingcomplex sheet profiles, such as are caused, among others, by irregularroll wear in the hot or cold reduction mills.

It is an object of this invention to overcome the flatness deficiencies,heretofore described, in :1 rolled sheet by providing a machine havingwork rolls which spontaneously and instantaneously adjust to the varyingconditions existing on the sheet and rolls during rolling, flatteningand related operations, and thus produce a sheet, strip or plate ofgreatly improved flatness.

More specifically, it is an object of this invention to produce arolling machine having work rolls or back-up rolls or both which enablethe work roll to eifect a relatively uniform percentage-wise reductionthroughout the cross-section of the sheet over its entire length and itis a related object of this invention to produce a rolling or flatteningmachine of the type described which yields sheet, strip or plate ofimproved flatness Without the need for use of manual or automaticcorrective adjustments of the types heretofore employed.

These and other objects and advantages of this invention willhereinafter appear and for purposes of illustration, but not oflimitation, embodiments of the invention are shown in the accompanyingdrawings, in which FIG. 1 is a schematic view of the roll section of arolling machine embodying the features of this invention;

FIG. 2 is a view similar to that of FIG. 1 showing a modification in themachine;

FIG. 3 is a sectional view of a machine roll fabricated in accordancewith the teachings of this invention;

FIG. 4 is a sectional view similar to that of FIG. 3 showing amodification in roll construction;

FIG. 5 is a sectional view similar to that of FIGS. 3 and 4 showing afurther modification in the roll construction; and

FIG. 6 is a force diagram showing the relative effect of sheet thicknesson reduction.

The objects of this invention are achieved by the design andconstruction of the rolls to elastically deform or give locally forinstantaneous change in profile in response to the profile of the sheet,strip or plate engaged thereby. It has been determined that the lowapparent rigidity of the roll assembly and its consequent ability toflex and self-adjust to the instantaneous sheet profile must be inducedartificially. For this purpose, the backing rolls should be made of amaterial having an apparent low spring-constant in compression and yetcapable of sustaining the high Hertzian contact pressure as well as theusual bending forces. While such materials do not exist in nature, animportant concept of this invention resides in the construction of a newand novel mill roll with the desired characteristics.

These can be achieved with a roll structure formed of a hard outercylindrical shell or sleeve 10 separated from a central arbor 12 by arelatively thin layer 14 of a low modulus resilient material, asrepresented by hard rubber or other elastomer, polyurethane, neoprene,butadiene-styrene or the like elastomeric materials, or other resilientplastic or foamed plastic materials such as the polyamides, polyesters,polypropylenes and the like.

The inner arbor 12 will be normally made of steel to support the bendingstresses. The outer shell can be made of hardened steel or even tungstencarbide, its outer surface constituting the working surface.

When the resilient interlayer 14 is formed of a cured or vulcanizedrubber or other elastic material, no obstruction need be provided at theends of the roll to confine the material. However, if the material iscapable of being squeezed out, it is desirable to confine the annularspace between the shell and arbor, such as by means of a rim 20 on theouter ends of the arbor or shell, as shown in FIG. 4, or by means of aclosure cap or sealing ring 22, held in place by a nut member or otherconventional capping means to form the composite roll, as illustrated inFIG. 5.

The thickness of the various elements making up the composite roll willdepend mainly upon the diameter of the roll and the hardness or strengthof the material of which it is formed. As a general guide, the shell 10should have a thickness to 3 the roll diameter and the resilientinterlayer 14 should have a thickness corresponding to about /2 to ofthe shell thickness. By way of illustration, in a back-up roll having atotal diameter of 52 inches, the thickness of the shell can be 5 inchesand the thickness of the resilient interlay 1 inch. In a back-up rollhaving a total diameter of 12 inches, the shell should typically have athickness of 1.5 inches and the resilient interlayer a thickness of0.375 inch. In a work or flexing roll having an overall diameter of 6inches, the shell thickness can be 1 inch and the thickness of theresilient interlayer can be A inch.

It is undesirable to make use of a material capable of fluid flow or asignificant amount of cold flow as the interlayer. It is preferred tomake use of a material having elastic memory so that it will functionnot unlike a fluid to distribute the rolling forces substantiallyuniformly along the sleeve thereby to relieve the roll of the bulkbending stresses transmitted to the arbor. Due to the low radialrigidity, the sleeve can deform elastically in response to smallvariations in thickness across the sheet. Such deformation, which canoccur immediately in response to differences in profile of the sheet,can take place much more easily and readily \in a roll structure of thetype described than in a solid steel roll of the same bulk. As a result,lower roll pressures will arise at the high spots in the sheet so thatthe percent reduction at the high spots will generally correspond to thepercent reduction at the lower spots. As a result, the high spots willnot be ironed out of the sheet as is the case with solid rolls and theresulting sheet will be relatively flat and free from buckles.

In the design of a reduction mill wherein a reduction pass is takenbetween work rolls 30, it is preferred to make use of the new and novelroll structures of this invention as the back-up rolls 32 and 34. Undersuch circumstances, thinner than usual work rolls can be employed inthemill since their lower flexural rigidity will not significantlyattenuate the described action of the composite back-up roll 32 or 34.Any thermal expansion gradients will readily be absorbed by a slightdistortion of the flexible sleeve 10- without significantly affectingthe contour or flatness of the delivered sheet 36.

It will also be understood that the resilient sleeved roll structure ofthis invention can be employed as the work roll 30 in a rolling mill, asshown in FIG. 2, or flattener, or as the flexing roll in a flattener, asof the types described in U.S. Patents No. 3,270,543 and No. 3,260,093,or that both the work rolls 30 and the back-up rolls 32-34 may beconstlucted of the composite rolls of this invention to provide stillgreater flexibility in the response and improved flatness in theproduct.

As a second application example, roller levelers for metal sheet orstrip, and especially tension levelers, will be used. In theiroperation, a number of problems have been encountered with equipment ofthe type heretofore employed.

At a fixed value of specific strip tension (p.s.i.) the permanentin-process extension of the material will be proportional to the ratioof its thickness and the diameter of the work roll. Thus, when a striphaving variations 4 in thickness across its width is leveled, bucklesappear along the thicker portions because of the greater amount ofextension, as previously described.

The theory that I have developed for the cause is as follows: Whilepassing over successive rollers of the leveler, the metal is plasticallybent and stretched. Since such deformations are relatively small, theneutral plane can be considered to be the same as the center plane. Ifthe thickness of the strip at the sections of greater thickness isdesignated by the letter T and at the thinner sections as T and if theradius of the work roll is designated by the letter R, the effectiveradius of curvature to which the strip is bent is at the thickersections and at the thinner sections. Since all the work rolls areparallel, the path through the leveler of the center plane of thethicker sections will be longer than the path of the thinner sections.Thus the thicker sections are extended by a greater amount by comparisonwith the thinner sections. By the same token, the thick longitudinalbelt is more taut than the thin and thus carries more tension in pounds.

With a composite roll of the type representative of the features of thisinvention, the higher tension can be utilized to suppress orsignificantly reduce the differential elongation of thick and thinmaterial. As seen in FIG. 6, the larger tensile force component N tendsto compress the roll diametrically and also to bend it and thereby toshorten the path of the material carrying the higher proportion of totaltension. Thus a phenomenon exists which tends to counteract excessiveextension of the thicker portion. To make use of this force, utilizationmust be made of working and/or backing rolls of the type describedhaving a much lower inherent rigidity or modulus than solid metal rollsof the type conventionally employed.

A composite roll with a resilient interayer 14 underlying the sleevesection 10 is much more responsive to small variations in force N bycomparison with soild steel rolls. Hence, such rolls flattenpreferentially at the locations of higher than average tension (in termsof pounds per unit width of strip) thereby reducing the excessive pathlength of material which otherwise would lead to excessive elongationand buckling or the like.

It will be apparent from the foregoing that I have provided a new andnovel means in the form of a roll structure which may be employed asback-up rolls or working rolls in a reduction roll mill, a flattener orlike machine to effect substantially uniform reduction in cross-sectionpercentage-wise across the width of a strip notwithstanding anydifferences in the profile or thickness across the strip thereby toproduce a product having improved flatness.

It will be understood that changes may be made in the details ofconstruction, arrangement and operation without departing from thespirit of the invention, especially as defined in the following claims.

I claim:

1. In a rolling machine for producing flat metal strip, a work roll overwhich the strip is flexed in pressure engagement, and one or moreback-up rolls in peripheral engagement with the periphery of the workroll on sides away from that engaged by the strip, said work roll havinga smooth outer peripheral work surface, at least one of said rollsincluding the work roll and back-up roll being formed of a hard outercylindrical shell, an inner ar-bor of cylindrical shape and aninterlayer between the shell and arbor formed of a low modulus elasticmaterial.

2. A machine as claimed in claim 1 in which the shell is of hardenedsteel.

3. A machine as claimed in claim 1 in which the interlayer is formed ofan elastic material which is incapable of fluid flow.

4. A machine as claimed in claim 1 in which the cpmposite roll comprisesa back-up roll for the working roll.

5. A machine as claimed in claim 1 in which the composite roll comprisesthe working roll.

6. A machine as claimed in claim 1 in which the composite roll comprisesboth a back-up roll and a working roll.

7. A composite roll as claimed in claim 1 in which the shell is of athickness within the range of 1 to of the roll diameter.

8. A composite roll as claimed in claim 1 in which the interlayer is ofa thickness within the range of /2 to A the thickness of the shell.

9. A composite roll as claimed in claim 1 in which the shell is formedof a hardened steel and the interlayer is formed of an orgaicelastomeric material.

References Cited UNITED STATES PATENTS CHARLES W. LANHAM, PrimaryExaminer B. I. MUSTAIKIS, Assistant Examiner

